LTE (Long Term Evolution), as a Long Term Evolution standard, enables study and commercialization of a new technology for a land mobile communications network to be carried out smoothly. An FD-MIMO (Full dimensional MIMO, full dimensional Multiple Input Multiple Output) antenna technology is introduced to LTE R13 (Release 13). To be specific, beamforming is performed in both a horizontal dimension and a vertical dimension with the help of a two-dimensional antenna array on a base station end, and corresponding precoding codebook enhancement, feedback procedure enhancement, and the like may be performed accordingly. A cell capacity is significantly improved through the enhancement. However, due to two-dimensional beamforming, when compared with R13 (Release 13), in R13, a precoding codebook is significantly increased, and a feedback procedure is also more complex. Therefore, a precoding feedback period is longer in R13, and an operation can often be performed only in a relatively static environment. For a high-speed movement scenario, to define a similar beamforming-based transmission solution, namely, an open-loop-3D-MIMO solution, has become an important issue to be discussed in LTE Release 14.
In an LTE standard, actually, some transmission modes for an open-loop high-speed movement scenario, for example, a transmission mode 2 (TM2), namely, SFBC (space frequency block coding) transmit diversity transmission and a transmission mode 3 (TM3), namely, LD-CDD (large delay cyclic delay diversity) transmission, have been defined in R8 (Release 8). Because channel estimation depends on a cell-specific reference signal, in the foregoing two transmission modes, transmission of signals of a maximum of only four antennas is allowed, and beamforming cannot be effectively performed to improve a cell capacity.
In the prior art, there is an open-loop-FD-MIMO related solution shown in FIG. 1. Specific steps in the solution are as follows:
Step 101: An eNB (evolved NodeB) sends a first reference signal on N dual-polarized antenna ports, namely, a first antenna group, for a terminal to estimate downlink channel states. Step 102: The terminal estimates the downlink channel states based on the first reference signal, to select a first beamforming codeword from a first codeword set, and calculate a channel quality indicator. Step 103: The eNB determines the first beamforming codeword based on a feedback of the terminal; performs beamforming for an antenna group (N/2 antenna ports) in each polarization direction, and generates two antenna ports, namely, a second antenna port group; and sends a second reference signal on the two antenna ports. Step 104: Perform LD-CDD precoding (a rank (rank)=2) or SFBC (a rank=1) on the two antenna ports, and generate two new ports or one new port, namely, a third antenna port group, for data transmission. Step 105: The terminal estimates downlink channel states on the two ports based on the second reference signal, to decode a data channel based on an inherent LD-CDD or SFBC coding procedure.
It can be learned from the foregoing steps that, in the prior art, beamforming is performed only for the antenna group in each polarization direction, and a beamforming vector is from the first codeword set. When the first codeword set is an R13 codebook, only one beam is generated through beamforming-based on the R13 codebook. Consequently, a spatial multipath characteristic cannot be well used. Even if a linear combination codebook in R14 is used, multipath random phase combination caused because of a fixed combined weight intensifies a channel fading characteristic. This departs from the original purpose of performing beamforming.